This invention is related generally to a lubrication system, more specifically to a lubrication system for bearings of a rotary machine such as a turbine power generator, and to a method of its modification.
In a conventional lubrication system for bearings of a rotary machine such as a turbine power generator, the lubricant oil supplied to the bearings returns to an oil tank through an oil returning mother pipe which is inclined downward in order to allow the oil to return to the tank smoothly and to prevent the oil from blowing out of the bearings. Then, a free surface of liquid oil is formed in the pipe, and the oil is collected in the tank, so that fire due to the oil blowout can be prevented. In addition, an air layer is formed above the free liquid oil surface due to the inclination of the pipe, and the air layer connects the turbine bearings and the oil tank. Therefor, the turbine bearings are kept under a negative pressure, because the tank is connected to an exhaust pump through an exhaust pipe and is kept under a negative pressure. Thus, the oil leakage from the bearings are prevented.
Now, a conventional lubrication system for bearings of a turbine generator of an electric power plant is discussed referring to FIGS. 1A and 1B. Referring to FIG. 1A, a typical turbine generator 1 has a plurality of bearings 3, although only one bearing 3 is shown in FIG. 1A for illustrative simplicity. Lubricant oil is supplied to the bearings 3 from an oil tank 2 through an oil supply pump 13 and an oil supply pipe 12. The lubricant oil returns to the oil tank 2 via an oil returning pipe 4 by gravity. The oil returning pipe 4 surrounds the oil supply pipe 12 forming a co-axial double pipe structure.
The oil returning pipe 4 includes outlet pipes 20 extending vertically downward from the bearings 3, and an oil returning mother pipe 21 for collecting oil from the outlet pipes 20 and delivering the oil to the oil tank 2. The oil returning mother pipe 21 is inclined downward to the oil tank 2.
As shown in FIG. 1A, a free liquid surface 22 is formed in the oil returning mother pipe 21 of the conventional lubrication system for the bearings of the turbine generator of the power plant. Thus, outflow of the oil from the bearings which are positioned above the oil liquid level is prevented.
In addition, the air space in the turbine bearings 3 and the air space in the oil tank 2 is communicated through the air above the free liquid surface 22 in the oil returning mother pipe 21, and the oil tank 2 is in a vacuum condition due to an exhaust pump 42 and an exhaust pipe 44 attached to the oil tank 2. Thus, the turbine bearings 3 are maintained in a vacuum condition, and outflow of the oil from the bearings are prevented more effectively.
However, in the conventional oil returning mother pipe 21 described above, the free liquid surface 22 is formed, and the upper part of the inner surface of the oil returning mother pipe 21 may rust. Thus, the oil returning mother pipe 21 deteriorates in years, and the rust gets mixed into the turbine oil, which would adversely affect the plant operation. Although stainless steel may be used for the oil returning mother pipes 21 to suppress rust in some cases, stainless steel is more difficult to be worked and more expensive compared to carbon steel. In addition, the conventional oil returning mother pipe 21 must have inclination toward the tank and must not have a reverse inclination to form the free liquid surface 22, which has resulted in strict restriction to the plant layout design.
Some efforts have been made for maintaining the inner surface of the oil returning mother pipe as disclosed in Japanese Utility Model Application Disclosure Jitsu-kai-Sho 63-34305 and in Japanese Utility Model Publication Jitsu-ko-Sho 61-14796, the disclosures of which are hereby incorporated by reference in their entirety. However, those known systems have dry areas in the upper part of the oil returning mother pipes which would result in the rust.